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Mr. Steve Magnuson May 5, 1987 Page 2 analyses on the same specimen before and after the Proctor test, and one direct shear test. Testing was conducted at the Lincoln-Devore, Inc. laboratory in Colorado Springs, Colorado. The test results indicate that the Standard Proctor dry density of the refuse is approximately 105 pcf with an optimum moisture content of approximately 10 percent. A small amount of particle breakdown was measured before and after the Proctor test (which resulted in a slight breakdown in gravel-sized particles and a five percent increase in percent passing the No. 200 sieve). The direct shear test yielded a peak strength of approximately 42 degrees and a residual strength of approximately 40 degrees. Cohesion measured in the test was 100 psf or less. The test was conducted on three specimens remolded to at least 90 percent of Standard Proctor density and at optimum moisture content. The specimens were saturated, then sheared under consolidated, drained conditions at normal stresses of 1.44, 3.6, and 7.2 ksf. The measured shear strength is typical of an angular, gravelly sand. METHOD OF STABILITY ANALYSIS Stability analyses were conducted along a two-dimensional section through the waste pile in its completed configuration. The section shown in Figure 1 (having the largest height of pile) was selected as the critical section for slope stability. Slope stability was evaluated by the modified Bishop method (Bishop, 1955), which is a widely used method and generally yields conservative results (Huang, 1983). Since the modified Bishop method employs circular failure surfaces, confirmation analyses were conducted using the Janbu method for non-circular surfaces (Janbu, 1973), in the event that non-circular surfaces would represent more critical stability conditions. Factors of safety calculated with the Modified Bishop method were slightly lower than those calculated with the Janbu method, and results presented in the remainder of this letter are from the Modified Bishop method calculations. The slope stability calculations were actually performed by the STABL2 computer program (Siegel, 1977). Modified Bishop and Janbu methods of evaluation are incorporated into the program. The STABL2 program uses a random failure surface generation routine, then calculates the factor of safety along the faiiure surface. For the results given below, the factor of safety shown is the minimum of at least 100 failure surfaces generated for each case. Seismic conditions were represented with pseudo-static analyses by an equivalent horizontal acceleration or seismic coefficient of 0.05 g. Pseudostatic analyses are appropriate for embankments that would not liquefy or exhibit a significant loss of shear strength with seismic shaking (Seed, 1979). The seismic coefficient of 0.05 was selected as a conservative value based upon a brief review of the seismicity of the site area from published literature (Kirkham and Rogers, 1981; U.S. Army Corps of Engineers, 1982; Uniform Building Code, 1976; Algermissen et al., 1982). u